The requirements facing today's internal combustion engines are increasing all the time. This applies both to internal combustion engines that operate with diesel fuel and to those that are powered by gasoline or other fuels. In addition to steadily increasing performance, a progressive reduction in harmful exhaust emissions is also demanded of the internal combustion engine.
Harmful exhaust gas emissions are reduced with the aid of low emission concepts. Technically these are based on the use of catalytic converters and broadband lambda probes, for example. However, the output signal of broadband lambda probes is subject to inaccuracies. In order to effectively compensate for said inaccuracies and to calibrate the broadband lambda probe used, DE-A-198 42 425 C2 discloses a method for correcting the characteristic curve of the lambda probe. Said correction or adjustment of the broadband lambda probe is performed during an overrun fuel cut-off phase of the internal combustion engine, i.e. without injection of fuel. This means that during said overrun fuel cut-off phase the value measured by the broadband lambda probe can be compared with the reference value for clean air. A calibration factor is determined in order to calibrate the measured value to the reference value for clean air. Owing to the simplicity and reliability of the method of DE-A-198 42 425 C2 it is employed in mass-produced motor vehicles.
It is however disadvantageous that with the method described by DE-A-198 42 425 C2 an influence of the humidity of the aspirated air of the internal combustion engine fails to be taken into account. According to manufacturer specifications of the broadband lambda probe, when saturated air at 30° C. is aspirated, for example, an inaccuracy of more than 4% is caused by the influence of the humidity of the air. This tolerance has a significant effect on the emissions of the internal combustion engine and consequently needs to be reduced.